My A.P.R.P. gets filtered morning and early afternoon sun and no evening sun and, since we're in a river valley near Vancouver, that is probably a lot less than what your tree gets in California. The Vertrees book "Japanese Maples" says the spring and early summer color of red-maroon holds well through hot weather, deepening in late summer to a more purplish tone. "In direct sun, it will bronze somewhat late in the season. However, the color holds much better and sunburns less than the older standard cultivar 'Atrolineare'." So, while the leaf form of yours suggests Red Pygmy, it doesn't have the expected color. Would we expect more greening of the leaves if you reduce the sun exposure? I am not anywhere close to expert but I wonder if this is a variation that is not true to type. Mine is a grafted specimen from a reliable supplier. Maybe your supplier would be willing to exchange if red is what you want.